Coordination Polymers Driven by Diamino-tetracarboxylates: Hydrothermal Assembly, Structural Features, and Catalytic Application

Eight new coordination polymers (CPs) were assembled by hydrothermal methods from 5,5′-(ethane-1,2-diylbis(azanediyl))diisophthalic acid (H4edda) as a primary diamino-tetracarboxylate building block. To facilitate the crystallization, various auxiliary N-donor ligands were also employed, ranging from 1,10-phenanthroline (phen), 2,2′-bipyridine (2,2′-bipy), and pyridine (py) to 4,4′-bipyridine (4,4′-bipy), 1,2-di(4-pyridly)ethylene (dpe), and 1,4-bis(pyrid-4-yl)benzene (bpb). The obtained compounds represent six 2D and two 3D coordination polymers, formulated as [Co(μ-H2edda)(μ-dpe)]n (1), [Mn(μ-H2edda)(μ-dpe)]n (2), [Cd(μ-H2edda)(μ-4,4′-bipy)]n (3), [Co2(μ4-edda)(phen)2(H2O)]n (4), [Co2(μ6-edda)(phen)2]n·6nH2O (5), [Zn2(μ4-edda)(2,2′-bipy)2(H2O)]n (6), [Ni2(μ4-edda)(μ-bpb)2(H2O)2]n·1.5n(bpb) (7), and [Zn2(μ6-edda)(py)(H2O)]n·3nH2O (8). These CPs were structurally characterized and analyzed by solid-state methods. In addition, the catalytic behavior of the obtained compounds was investigated in the Knoevenagel condensation of aldehydes as a model reaction. Remarkably, catalysts 6 and 8 exhibited a particularly significant activity, stability, and reusability in the condensation of pyridine-3-aldehyde with malononitrile, leading to an almost quantitative product yield (99%) under optimized conditions. This study contributes to the molecular design of functional coordination polymers driven by flexible diamino-tetracarboxylate building blocks.